This invention relates to a method for the therapeutic treatment of nearsightedness and a visual acuity chart used therefor, and more particulary to a method for therapeutic treatment of nearsightedness by relaxing the abnormal tension of the ciliary muscle of the eye which causes the nearsightedness as well as to a visual acuity table which is specifically employed in the above method.
The general structure of the eye which occupies an essential part in the description of this invention is explained before the method of this invention is described in detail.
It is well known that the eye mainly comprises a cornea 1 which is the forwardmost surface of the eyeball, an iris 2 which is located in back of the cornea, a lens which is shaped like a concave artificial lens 3, a ciliary body 4 which includes the ciliary muscle, vitreous body 5 which is transparent and the retina 6. The cornea maintains the fixed shape of the eyeball and focuses light rays onto the fundus by reflecting them; the iris works like an adjustable diaphragm in a camera to increase and decrease the amount of light reflected into the eye from the object which is seen.
The lens 3 adjusts and reflects the incoming light in conjunction with the cornea 1 in such a way that the intensity of reflection of the lens is adjustable corresponding to the distance between the nearby or distant object which is seen and the eyeball so that the clear image is focused on the retina of the eyeball. The ciliary body adjusts the thickness of the lens by contracting or elongating the lens using the ciliary muscle, and the retina receives the light energy passed through the lens and transforms it into a nerve stimulus, which in turn is transferred to the brain by nerve fibers.
Nearsightedness is a phenomenon in which the ciliary muscle of the ciliary body is abnormally strained and accordingly the suspensory ligament is relaxed causing the lens to become thicker whereby the incoming light is focused in front of the retina and the retina receives obscure images.
To rectify nearsightedness, glasses which comprise a pair of concave artificial lenses are employed so that the light rays reflected from objects are properly focused on the retina.
While farsightedness, hyperopia is a phenomenon in which the ciliary muscle is abnormally relaxed causing the lens to become thinner whereby the incoming light rays are focused in back of the retina and the retina again receives obscure images.
To rectify the farsightedness, glasses which comprise a pair of convex artificial lenses are employed so that the light rays reflected from objects properly focuses on the retina.
The following are the main reasons for nearsightedness;
A long period of close work which compels a person to constantly look at an object which is within 40cm from the eyes, fatigue of the eyes, a nutritionally unbalanced diet, and an internal or hereditary disease.
Nearsightedness of myopia takes several steps to develop: there is stationary myopia in the elementary stage, a refractive myopia in the secondary stage, an axial myopia in the third stage, and the detachment of the retina in the final stage. Stationary myopia is a phenomenon in which the lens stays abnormally thick due to long abnormal strain of ciliary muscle caused by continuous close work and the lens will become only slightly thinner even if the eyes try to observe distant objects. Refractive myopia is a more advanced phenomenon in which the reflection of the incoming light is no longer adjustable and also the structure of the retina has become abnormal. Axial myopia is a further advanced phenomenon in which the lens becomes extremely and abnormally thick and the shape of the eyeball becomes elliptical due to an elongation of the eyeball. When axial myopia is further developed, detachment of the retina occurs resulting in the loss of visual acuity.
Genuine myopia is a general term for refractive myopia and axial myopia.
In general, myopia appears in a complex form of stationary myopia and genuine myopia.
Stationary myopia and some cases of genuine myopia are subject to the application of the method of this invention.
Attendant to myopia are the problems such as the inconveniency of wearing glasses, lowered efficiency of study or work both of which result in causing a person to have a depressed personality.
Conventional treatments of myopia which have been developed and practiced are as following:
chemical treatment such as the use of eyedrop solutions,
physical treatment such as the application of supersonic waves,
surgical treatment such as the removal of the lens, and
treatment of recovering visual acuity by suitable exercises.
However, attendant to each above treatment is a problem such as the dependancy on eye drop solutions, the prolonged use of which may be hazardous to the eye, the loss of the accommodation function due to the surgical operation, and the necessity of using expensive instruments as in the case of treatment with sonic waves.
Therefore, a method for treatment of myopia which has no attendant difficulty has been desired by those who are skilled in the art.
Conventionally, there have been two theories regarding the relationship between the ciliary body (ciliary muscle) and myopia. One theory proclaims that the ciliary body is an involuntary muscle and therefore is not subject to the autonomic nervous system which is controlled by the parasypathetic nerves so that the myopia is completely hereditary and is not curable. Another theory proclaims that the ciliary muscle is subject to two nervous systems, that is, the contraction of the ciliary muscle is caused by the parasypathetic nerves and the relaxation of the ciliary muscle is caused by the sympathetic nerves, so that the myopia is curable.
According to a recent theory, it has been clarified by experiments that although the ciliary muscle is an involuntary muscle, it is subject to the integration of the neocortex cerebri system as well as the limbic system.
The present invention provides a new ocular device which may be used most effectively in the methodology relating to the therapeutic treatment of myopia.
Accordingly, it is an object of the invention to provide a visual acuity chart so that visual acuity can be reliably checked and measured without inaccurate results occuring due to the patient's memorizing in advance the sizes and locations of breaks of Landolt's rings, since the sizes and locations of the breaks of the rings can be easily changed at any time.
It is also an object of the invention to provide a visual acuity chart which can be employed for the therapeutic treatment of nearsightedness.